4 HUMAN HEALTH RISK ASSESSMENT

4.1 Introduction

4.1.1.1 With reference to Clause 3.4.7 of EIA Study Brief No. ESB-169/2007 for this Project, the human health risk assessment (HHRA) can be broadly grouped into the following tasks:-

(i) Assess the potential health impacts of the aerial emissions from STF during the operational phase;

(ii) Assess the potential health impacts of the operations associated with dewatered sewage sludge due to microbial emissions;

(iii) Assess the potential health impacts due to radon emissions associated with pulverized fly ash (PFA) arising from the construction and operation of STF; and

(iv) Assess the potential health impacts of the operations associated with incineration by-products arising from the operation of STF.

4.1.1.2 In light of the results of previous environmental assessments for incinerator projects[1], residual waste impact (including human health impact) arising from the operations associated with incineration by-products of STF was considered to be minimal and acceptable, provided that the following conditions would be fulfilled:-

l The incineration by-products comply with the proposed Incineration Residue Pollution Control Limits (refer to Section 5.4.2 of this EIA Report); and        

l The proposed mitigation measures for incineration by-products management activities are properly adopted.

4.1.1.3 Further details on the management of incineration by-products are presented in Section 5 of this EIA report. 

4.2 HHRA for Aerial Emissions from STF

4.2.1 Assessment Approach

4.2.1.1 There are five phases in the HHRA for aerial emissions from STF, which are shown as follows:

l Hazard Identification

l Exposure Assessment

l Dose-response Assessment

l Risk/hazard Characterization

l Uncertainty Interpretation

4.2.1.2 Details of the assessment methodology and findings for the HHRA for aerial emission from STF are presented in the following sub-sections. 

4.2.2 Hazard Identification

4.2.2.1 This stage involves identifying contaminants of concern (COCs) which would be released from the STF chimney and potential human receptors which would be exposed to the COCs.

COCs Identification

4.2.2.2 The air pollutants (individual chemicals) covered in Annex 1 of EPD’s “A Guidance Note on the Best Practicable Means for Incinerator (Municipal Waste Incineration) BPM 12/1” are identified as COCs and their health impacts are further assessed in the later stage of this HHRA. 

4.2.2.3 EPD’s BPM 12/1 aims to prevent the emissions of air pollutants of incinerators from harming the environment and human health or creating nuisance.  As a result, Annex 1 of BPM 12/1 should cover an adequate range of pollutants, which their emission levels need to be controlled to achieve the above aim.  Comparison of the BPM standard with overseas standards are provided in Section 3 of this EIA Report and it is considered appropriate to adopt the pollutant list in BPM 12/1 as COC in this HHRA.

4.2.2.4 The identified COCs and their health hazards are presented in Table 4.1.

Table 4.1         Identified COCs and Associated Health Hazards

Identified COC for HHRA	Classified as Carcinogen	Other Health Impact
Particulate	No	Respirable fraction of particulates has effects on health including respiratory illness, reduced lung function, morbidity and mortality rates increase at higher levels
Organic Compound	No	Certain organic compounds can give rise to odour nuisance and some have health effects on human
Hydrogen chloride (HCl)	No	Corrosion to skin, eyes and respiratory tract.  At high concentration can cause pulmonary oedema and laryngeal spasms
Hydrogen fluoride (HF)	No	Irritation to skin, eyes and respiratory tract.  Repeated over-exposure may cause damage to the lungs, liver and kidneys
Sulphur dioxide (SO2)	No	At high concentration can cause bronchoconstriction and chemical bronchitis and tracheitis
Nitrogen oxides (expressed as nitrogen dioxide (NO2)	No	Long term effects of NOx exposure occur primarily in the lung, but also include spleen, liver and blood toxicity
Carbon monoxide (CO)	No	Binds to the blood haemoglobin, greatly reducing the red blood cell’s ability to transport oxygen to body tissues.  Effects may include headaches, dizziness, convulsions, at high concentration loss of consciousness and death
Cadmium (Cd)	Yes	Long term effect of Cd inhalation may include bronchitis, emphysema and anaemia
Thallium (Tl)	No	Exposure can lead to pulmonary edema, convulsions, psychosis, liver and kidney damage
Mercury (Hg)	No	Exposure of Hg vapour may induce effects on nervous system, oral mucosa and kidneys
Antimony (Sb)	No	Inhalation of dust and fumes can cause nose and throat irritation, inflammation of respiratory tract, pneumonitis, ulceration and perforation of the nasal septum, headaches, dyspnea, vomiting and diarrhea
Arsenic (As)	Yes	Ulceration of nasal septum, peripheral neuropathy, respiratory irritation
Lead (Pb)	Yes	Long term Pb exposure appears to cause increase in blood pressure and hypertension in adults.  Short term exposure to high Pb levels can cause tiredness, irritability, abdominal pain and anaemia
Chromium (Cr)	Yes	Causes liver necrosis and nephritis
Cobalt (Co)	No	Causes decreased pulmonary function, weight loss, dermatitis, diffuse nodular fibrosis, respiratory hypersensitivity and asthma
Copper (Cu)	No	Intake of excessively large doses of Cu causes effects via oral exposures such as mucosal irritation / corrosion, capillary damage, liver and kidney toxicity and disruption of the central nervous system
Manganese (Mn)	No	Inhalation of Mn may cause pneumonia and bronchitis as well as changes in blood flow / chemistry
Nickel (Ni)	Yes	Sensitization dermatitis, allergic asthma, pneumonitis
Vanadium (V)	No	Cough, fine rales, wheezing, bronchitis, dyspnea and eczema.  Inhalation of V may also cause pneumonitis and bronchopneumonitis
Polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) (expressed as TCDD equivalent)	Yes	The effects of long term exposure to dioxins include chloracne, liver damage, reproductive toxicity and depression of the immune system

Human Receptors Identification

4.2.2.5 Air Sensitive Receivers (ASRs) in the vicinity of STF are identified as potential human receptors since inhalation pathway would be the only exposure pathway to COCs emitted from STF.  The ASRs (potential human receptors) are identified in the air quality impact assessment (Section 3) of this EIA and are presented in Table 4.2.

Table 4.2         Identified Potential Human Receptors

ASR	Description	Land Use	Near Filed / Far Field
A1	Ngau Hom Sha	Residential	Near Field
A2	West Ha Pak Nai	Residential	Near Field
A3	West Ha Pak Nai	Residential	Near Field
A4	West Ha Pak Nai	Residential	Near Field
A5	East Ha Pak Nai	Residential	Near Field
A6	Black Point Power Station (Office)	Industrial	Near Field
A7	EPD WENT Landfill Site Office	Industrial	Near Field
A8	Lung Kwu Sheung Tan	Residential	Near Field
A9	Sheung Pak Nai	Residential	Near Field
A10	Tin Shui Wai Park	Recreational	Far Field
A11	Pak Long	Residential	Far Field
A12	Leung King Estate	Residential	Far Field
A13	Tsing Shan Monastery	GIC	Far Field
A14	Siu Shan Court	Residential	Far Field
A15	Butterfly Beach Park	Recreational	Far Field
A16	San Shek Wan	Residential	Far Field
A17	Tuen Mun Area 38	Residential	Far Field
A18	Green Island Cement (Office)	Industrial	Far Field
A19	Site Office of Castle Peak Power Company Limited	Commercial	Far Field
A20	Site Office of Eco Park	Commercial	Far Field
A21	Lung Kwu Tan	Residential	Far Field
A22	Temple near the Tsang Tsui Ash Lagoons	Place of public worship	Near Field
A23	Site Office of Shiu Wing Steel Mill	Commercial	Far Field
A24	Siu Lung Court	Residential	Far Field
A25	On Ting Estate	Residential	Far Field
A26	Yau Oi Estate	Residential	Far Field
A27	Tuen Mun Town Plaza	Residential	Far Field
A28	S.K.H. St. Simon’s Lui Ming Choi Secondary School	Education Institution	Far Field
A29	Hong Lai Garden	Residential	Far Field
A30	Tai Hing Garden	Residential	Far Field
A31	Chelsea Heights	Residential	Far Field
A32	Melody Garden	Residential	Far Field

4.2.3 Exposure Assessment

4.2.3.1 This stage involves the following tasks:-

l Determination of COC concentrations at identified potential human receptors; and

l Characterization of potential human receptors.

Determination of COC Concentrations

4.2.3.2 The cumulative COC concentrations at the identified representative ASRs are predicted as part of the air quality impact assessment in Section 3 of this EIA Report.  The predicted short-term and long-term average COC concentrations at the representative ASRs are shown in Appendix 3.16.  

Characterization of Potential Human Receptors

4.2.3.3 Inhalation is the only exposure pathway considered for the COC emitted from the stack emission of STF.  This is in line with the previous local studies on incinerator projects, where all the studies assessed the potential impact arising from incinerators located at/near the proposed site for the STF.   

4.2.3.4 Characteristics of potential human receptors need to be determined before the COC exposure dose can be calculated.  The values of various characteristic parameters are adopted from USEPA (2005) and presented in Table 4.3.

Table 4.3         Human Receptor Characteristic Parameter Values

Characteristic Parameter	Value Adopted	Unit
Exposure frequency	350	day/yr
Exposure duration^a	20 (design life)^b	yr
Averaging time	70	yr

a)    Exposure frequency for off-site workers will be determined based on number of working days

b)    Design life of 20 years for the STF should be set as a condition since the health risk will be underestimated if STF continues to operate beyond the design life.          

4.2.4 Dose-response Assessment

4.2.4.1 This stage involves determination of the three relationships as stated below:-

l Relationship between the carcinogenic COC exposure and response in human;

l Relationship between long term COC exposure and non-carcinogenic health effect in human; and

l Relationship between acute COC exposure and non-carcinogenic health effect in human.

Carcinogenic COC Exposure and Response in Human

4.2.4.2 Exposure of carcinogenic COCs would increase the risk of cancer development and the relationship between the dose and human response is expressed in terms of unit risk factor (URF).  Inhalation URF for the carcinogenic COCs documented in WHO (2000), OEHHA (2005b) and IRIS database maintained by USEPA were reviewed.  The adoption of URFs for individual carcinogenic COC follows the following hierarchy:-

l WHO recommended URFs;

l USEPA recommended URFs (from IRIS database); and

l California EPA recommended URFs (from OEHHA).

4.2.4.3 Table 4.4 summarizes the URFs for carcinogenic COCs, in which the selected URFs are typed in bold.

Table 4.4         Inhalation Cancer Slope Factor and Unit Risk Factor for Carcinogenic COCs

Carcinogenic COCs	Unit Risk Factor (μg/m^3)^-1
	OEHHA (2005)	WHO (2000)	IRIS
Cd	4.2 x 10^-3	-	1.8 x 10^-3
As	3.3 x 10^-3	1.5 x 10^-3	4.3 x 10^-3
Pb	1.2 x 10^-5	-	-
Cr (VI)	1.5 x 10^-1	4 x 10^-2	1.2 x 10^-2
Ni	2.6 x 10^-4	3.8 x 10^-4	2.4 x 10^-4
Dioxins	38	-	-

Long Term COC Exposure and Non-carcinogenic Health Effect in Human

4.2.4.4 The non-carcinogenic effects posed by long term exposure of COCs via inhalation pathway are determined by comparing the predicted COC concentrations at the worst-impacted human receptor with appropriate standards which are established to protect the human health.  Given that the concentration of a particular COC is found to be lower than the corresponding standard, the non-carcinogenic health impact due to exposure of the COC would be considered to be insignificant.  

4.2.4.5 The guideline values of the Hong Kong Air Quality Objectives (HKAQO) are adopted for COCs if available.  If guideline values are not available for any particular COC, air quality standard is adopted under the following hierarchies:-

l WHO recommended air quality standard;

l USEPA recommended air quality standard (inhalation reference concentration from IRIS database); and

l California EPA recommended air quality standard (chronic reference exposure level from OEHHA).

4.2.4.6 There is no air quality standard / guideline established for some COCs.  In this case, modification of occupational exposure limits (OELs) for these COCs were made to derive the “Chronic Exposure Air Quality Standard” (CEAQS) for use in this HHRA.  Occupational exposure standards in the UK were used to derive the standard for long term exposure.  There are two types of OELs, namely occupation exposure standards (OESs) and maximum exposure limits (MELs).  The requirements for compliance are more stringent for MELs, which are set for those chemicals liable to have serious health implications for workers.   In this study, CEAQSs for COCs were derived based on OES/100 or MEL/500.

4.2.4.7 Table 4.5 presents the long term air quality standards/occupational exposure limits reviewed and the values selected/derived for comparison with the predicted COC concentrations at the worst-impacted human receptor.

Table 4.5         Air Quality Standards/Occupational Exposure Limit Value for COCs Long Term Exposure

COCs	Air Quality Standard / Occupational Exposure Limit Value (μg/m^3)	Averaging Time	Country / City	Source ^(a)	Value Adopted / Derived (μg/m^3)	Note
Sb	500 (MEL)	8-hr Time Weighted Average (TWA)	UK	HSE (2002)	1 (=500/500)	b, c, d, e
As	0.03	Chronic Exposure	California	OEHHA (2005)	0.03	b, c, d
CO	No guideline	-	-	-	-	b, c, d, e
Cd	0.005* 0.02	Annual Chronic Exposure	WHO standard California	WHO (2000) OEHHA (2005)	0.02	b, d
Cr (VI)	0.008 (chromic acid mists and dissolved Cr VI aerosols) 0.2 (as Cr VI)	Chronic Exposure Chronic Exposure	IRIS inhalation reference concentration (RfC) California	IRIS OEHHA (2005)	0.008	b, c
Co	100 (MEL)	8-hr TWA	UK	HSE (2002)	0.2 (=100/500)	b, c, d, e
Cu	200 (OES)	8-hr TWA	UK	HSE (2002)	2 (=200/100)	b, c, d, e
Dioxins	0.00004	Chronic Exposure	California	OEHHA (2005)	0.00004	b, c, d
HCl	20 9	Chronic Exposure Chronic Exposure	IRIS RfC California	IRIS OEHHA (2005)	20	b, c
HF	14 1,500 (OES)	Chronic Exposure 8 -hr TWA	California UK	OEHHA (2005) HSE (2002)	14	b, c, d
Pb	1.5	3-month	Hong Kong	HKAQO	1.5	d, e
Mn	0.15 0.05 0.2	Annual Chronic Exposure Chronic Exposure	WHO standard IRIS RfC California	WHO (2000) IRIS OEHHA (2005)	0.15	b
Hg	1 0.3 (elemental Hg) 0.09	Annual Chronic Exposure Chronic Exposure	WHO standard IRIS RfC California	WHO (2000) IRIS OEHHA (2005)	1	b
NOx, as NO2	80	Annual	Hong Kong	HKAQO	80	d, e
Ni	0.05 (except NiO2) 0.1 (NiO2)	Chronic Exposure	California	OEHHA (2005)	0.05	b, c, d
Particulates	55	Annual	Hong Kong	HKAQO	55	c, d, e
SO2	80	Annual	Hong Kong	HKAQO	80	d, e
Tl	100 (OES)	8-hr TWA	UK	HSE (2002)	1 (=100/100)	b, c, d, e
V	50 (MEL)	8-hr TWA	UK	HSE (2002)	0.1 (=50/500)	b, c, d, e

Notes

* The guideline value by WHO is based on the prevention of further increase of cadmium in agricultural soils, which is considered not applicable to the risk assessment for the current study.

(a) Sources of References:

HKAQO: http://www.epd-asg.gov.hk/english/backgd/hkaqo.php

WHO (2000): http://www.euro.who.int/document/e71922.pdf

USEPA (IRIS): http://cfpub.epa.gov/ncea/iris/index.cfm

OEHHA(2005): http://www.oehha.ca.gov/air/chronic_rels/AllChrels.html

HSE (2002): Health and Safety Executive (2002). EH40/2000 Occupation Exposure Limits 2002

(b) No chronic exposure guideline value in HKAQO

(c) No chronic exposure guideline value in WHO

(d) No chronic exposure guideline value in USEPA (IRIS)

(e) No chronic exposure guideline value in OEHHA

Acute COC Exposure and Non-carcinogenic Health Effect in Humans

4.2.4.8 Similar to long term COC exposure, the non-carcinogenic effects posed by acute exposure of COCs via inhalation pathway are determined by comparing the predicted COC concentrations at the worst-impacted human receptor (1-hr average concentration) with appropriate exposure limits / reference levels.  Given that the concentration of a particular COC is found to be lower than the corresponding exposure limits / reference levels, the non-carcinogenic health impact due to exposure of the COC would be considered to be insignificant.

4.2.4.9 The HKAQO guideline values are adopted for COCs listed in HKAQO with 1-hour standard.  For other COCs, the following hierarchy, which is recommended in USEPA (2005), is adopted to select the exposure limits/reference levels as follows:

l WHO

l USEPA (IRIS database)

l Cal/EPA Acute RELs

l AEGL-1

l ERPG-1

l TEEL-1

l AEGL-2

4.2.4.10 If no AEGL-1 value is available, but an AEGL-2 value is available, selected the AEGL-2 only if it is a more protective value (lower in concentration) than an ERPG-1, or a TEEL-1 value if either of these values is available.

4.2.4.11 The adopted exposure limits/reference levels for acute exposure of COCs are presented in Table 4.6.

Table 4.6         Exposure Limits/Reference Levels for COCs Acute Exposure

COC	Exposure Limit/Reference Level (μg/m^3, 1-hr averaging time)	Source ^(a)	Note
Sb	1,500/10 = 150	TEEL-1	c, e
As	30 /10 = 3	TEEL-1	c, e
CO	30,000	HKAQO
Cd	30/10 = 3	TEEL-1	c, e
Cr (VI)	30/10 = 3	TEEL-1	c, e
Co	3,000/10 = 300	TEEL-1	c, e
Cu	100	Cal/EPA Acute REL	b
Dioxins	No guideline	-	d
HCl	2,100	Cal/EPA Acute REL	b
HF	240	Cal/EPA Acute REL	b
Pb	150/10 = 15	TEEL-1	c, e
Mn	3,000/10 = 300	TEEL-1	c, e
Hg	1.8	Cal/EPA Acute REL	b
NOx, as NO2	300	HKAQO
Ni	6.0	Cal/EPA Acute REL	b
Particulates	No guideline	-	c
SO2	800	HKAQO
Tl	300/10 = 30	TEEL-1	c, e
V	150/10 = 15	TEEL-1	c, e

Notes:

(a)    Sources of References:

HKAQO: http://www.epd-asg.gov.hk/english/backgd/hkaqo.php

WHO: http://www.euro.who.int/document/e71922.pdf

USEPA: http://cfpub.epa.gov/ncea/iris/index.cfm

Cal/EPA Acute REL http://www.oehha.ca.gov/air/acute_rels/allAcRELs.html

AEGL-1: http://www.epa/gov/opt/aegl/pubs/chemlist.htm

ERPG-1: http://www.aiha.org/1documents/Committees/ERP-erpglevels.pdf

TEEL-1: http://www.hss.energy.gov/HealthSafety/WSHP/chem_safety/teel.html

AEGL-2: http://www.epa/gov/opt/aegl/pubs/chemlist.htm

(b)   No acute exposure guideline value in HKAQO, WHO and USEPA

(c)    No acute exposure guideline value in HKAQO, WHO, USEPA, Cal/EPA Acute REL, AEGL-1, AEGL-2 and ERPG-1

(d)   No acute exposure guideline value in all the above references sources.

(e)    With reference to the Haber Rule, calculation of the 1-hour acute exposure limit/reference level from 15-minute acute exposure limit/reference level should be derived by (TEEL-1)/4. As a conservative approach, (TEEL-1)/10 has been adopted as the acute exposure limit/reference level.

4.2.5 Risk/Hazard Characterization

4.2.5.1 Three types of risk/hazard are characterized in this HHRA, as shown in the followings:

l Cancer risk due to exposure to carcinogenic COCs;

l Non-carcinogenic health hazard due to long term exposure to COCs; and

l Non-carcinogenic health hazard due to acute exposure to COCs.

Cancer Risk

4.2.5.2 The lifetime individual excess cancer risk[2] is calculated by the following equations, adopted from USEPA (2005):

Cancer Risk_inh(i) = [(C_i x EF x ED) x URF_i] / (AT x 365 day/yr)............. Equation 4.1

                        where

Cancer Risk_inh(i)        =    lifetime individual excess cancer risk through direct inhalation of carcinogenic COC_i

C_i =    air concentration of COC_i at potential human receptor (μg/m³)

EF                          =    exposure frequency (day/yr)

ED                         =    exposure duration (yr)

AT                         =    averaging time (yr)                               

URF_i =    Unit risk factor of COC_i

Total Cancer Risk_inh = Σ (Cancer Risk_inh(i))............................................ Equation 4.2

                        where

Total Cancer Risk_inh = lifetime individual excess cancer risk through direct inhalation of all carcinogenic COCs

4.2.5.3 The risk assessment criteria for cancer risk from exposure to carcinogenic COCs emitted from the stack of STF are presented in Table 4.7.

Table 4.7         Risk Assessment Criteria for Cancer Risk

Acceptability of Cancer Risk	Estimated Lifetime Individual Excess Cancer Risk
Significant	> 10^-4
Risk should be reduced to “As Low As Reasonably Practicable” (ALARP)	> 10^-6to 10^-4
Insignificant	£ 10^-6

4.2.5.4 By applying the air quality assessment results presented in Appendix 3.16 to Equation 4.1 above, the cumulative cancer risk arising from exposure to carcinogenic COCs by the impacted human receptor can be calculated. 

4.2.5.5 The lifetime individual excess cancer risks arising from STF for the impacted human receptors are presented in Table 4.8.  The highest cancer risk arising from STF is predicted to be 1.51E-5 and is considered to be in “As Low As Reasonably Practicable” (ALARP) level.

Table 4.8         Cancer Risk Arising from Carcinogenic COCs Exposure from STF

Near Field/ Far Field	Air Sensitive Receiver (ASR)	Lifetime Individual Excess Cancer Risk						Total Lifetime Individual Excess Cancer Risk
		Cd	As	Pb	Cr (VI)	Ni	Dioxins
Near Field	A1	9.86E-09	8.63E-08	6.90E-10	2.30E-06	2.19E-08	4.37E-10	2.42E-06
	A2	6.41E-08	5.38E-07	4.31E-09	1.44E-05	1.36E-07	2.72E-09	1.51E-05
	A3	6.41E-08	5.26E-07	4.21E-09	1.40E-05	1.33E-07	2.66E-09	1.48E-05
	A4	3.45E-08	3.04E-07	2.43E-09	8.11E-06	7.70E-08	1.55E-09	8.53E-06
	A5	5.42E-08	4.44E-07	3.55E-09	1.18E-05	1.12E-07	2.25E-09	1.25E-05
	A6	2.96E-08	2.59E-07	2.07E-09	6.90E-06	6.56E-08	1.31E-09	7.26E-06
	A7	0.00E+00	1.64E-08	1.32E-10	4.38E-07	4.16E-09	7.29E-11	4.59E-07
	A8	4.44E-08	3.70E-07	2.96E-09	9.86E-06	9.37E-08	1.87E-09	1.04E-05
	A9	1.48E-08	1.15E-07	9.21E-10	3.07E-06	2.92E-08	5.73E-10	3.23E-06
	A22	2.47E-08	1.97E-07	1.58E-09	5.26E-06	5.00E-08	1.00E-09	5.53E-06
Far Field	A10	5.71E-09	4.76E-08	3.81E-10	1.27E-06	1.21E-08	2.41E-10	1.34E-06
	A11	1.11E-08	9.28E-08	7.43E-10	2.48E-06	2.35E-08	4.70E-10	2.60E-06
	A12	7.27E-09	6.06E-08	4.85E-10	1.62E-06	1.53E-08	3.07E-10	1.70E-06
	A13	6.04E-09	5.03E-08	4.03E-10	1.34E-06	1.27E-08	2.55E-10	1.41E-06
	A14	4.03E-09	3.36E-08	2.69E-10	8.96E-07	8.51E-09	1.70E-10	9.42E-07
	A15	4.56E-09	3.80E-08	3.04E-10	1.01E-06	9.63E-09	1.93E-10	1.07E-06
	A16	5.44E-09	4.53E-08	3.63E-10	1.21E-06	1.15E-08	2.30E-10	1.27E-06
	A17	6.04E-09	5.03E-08	4.03E-10	1.34E-06	1.27E-08	2.55E-10	1.41E-06
	A18	6.45E-09	5.37E-08	4.30E-10	1.43E-06	1.36E-08	2.72E-10	1.51E-06
	A19	7.51E-09	6.26E-08	5.01E-10	1.67E-06	1.59E-08	3.17E-10	1.76E-06
	A20	6.12E-09	5.10E-08	4.08E-10	1.36E-06	1.29E-08	2.58E-10	1.43E-06
	A21	9.63E-09	8.02E-08	6.42E-10	2.14E-06	2.03E-08	4.06E-10	2.25E-06
	A23	6.29E-09	5.24E-08	4.19E-10	1.40E-06	1.33E-08	2.65E-10	1.47E-06
	A24	3.73E-09	3.11E-08	2.49E-10	8.29E-07	7.87E-09	1.57E-10	8.72E-07
	A25	3.90E-09	3.25E-08	2.60E-10	8.68E-07	8.24E-09	1.65E-10	9.13E-07
	A26	4.04E-09	3.36E-08	2.69E-10	8.97E-07	8.52E-09	1.70E-10	9.44E-07
	A27	4.25E-09	3.54E-08	2.84E-10	9.45E-07	8.98E-09	1.80E-10	9.94E-07
	A28	4.14E-09	3.45E-08	2.76E-10	9.19E-07	8.73E-09	1.75E-10	9.67E-07
	A29	4.53E-09	3.78E-08	3.02E-10	1.01E-06	9.57E-09	1.91E-10	1.06E-06
	A30	4.91E-09	4.09E-08	3.27E-10	1.09E-06	1.04E-08	2.07E-10	1.15E-06
	A31	5.14E-09	4.28E-08	3.43E-10	1.14E-06	1.09E-08	2.17E-10	1.20E-06
	A32	4.37E-09	3.65E-08	2.92E-10	9.72E-07	9.23E-09	1.85E-10	1.02E-06

Non-carcinogenic Health Impact due to Long Term Exposure to COC

4.2.5.6 As discussed above, the non-carcinogenic health impact posed by long term exposure of COCs is determined by comparing the predicted COC concentrations with the adopted/derived reference levels presented in Table 4.9.  The background concentrations of the COC assumed in this assessment are also shown in Table 4.9.  If the concentration of a particular COC is found to be lower than the corresponding adopted/derived reference level, the non-carcinogenic health impact would be considered to be insignificant.

4.2.5.7 Table 4.10 and Table 4.11 present the assessment result for cumulative non-carcinogenic health impact due to long term COC exposure by the worst-impacted human receptor in the near field and far field areas respectively.  The cumulative non-carcinogenic health impact includes the impact arising from STF as well as other major existing and planned emission sources considered in the air quality impact assessment plus the background contribution.

4.2.5.8 Cumulative long term health impact of the STF with all relevant existing, committed and planned sources imposed to the impact human receptors are assessed and compared with the guidelines adopted.  It is concluded that the levels of non-carcinogenic chemicals were found to be insignificant comparing  to the adopted/derived reference levels.

Non-carcinogenic Health Impact due to Acute Exposure to COC

4.2.5.9 Non-carcinogenic health impact posed by acute exposure of COCs is determined by comparing the predicted COC concentrations with exposure limits/reference levels adopted which are presented in Table 4.12.  The background concentrations of the COC assumed in this assessment are also shown in Table 4.12.  If the concentration of a particular COC is found to be lower than the corresponding standard, the non-carcinogenic health impact would be considered to be insignificant.

4.2.5.10 Table 4.13 and Table 4.14 present the assessment results for non-carcinogenic health impact due to acute COC exposure by the worst-impacted human receptor in the near field and far field areas respectively.  The cumulative non-carcinogenic health impact includes the impact arising from STF as well as other major existing and planned emission sources considered in the air quality impact assessment plus the background contribution.

4.2.5.11 Cumulative acute health impact of the STF with all relevant existing, committed and planned sources imposed to the worst impact human receptors are assessed and compared with the guidelines adopted.  It is concluded that the effect are insignificant when compared to the proposed exposure limits/reference level. 

4.2.6 Conclusions

4.2.6.1 A health risk assessment for the aerial emission from the STF during the operation phase has been undertaken.  The cumulative cancer risk of STF was found to be tolerable and at the risk level of “As Low As Reasonably Practicable” (ALARP).  For both cumulative acute and long term non-carcinogenic health impact, the levels of non-carcinogenic chemicals were found to be insignificant when compared to the adopted/derived reference levels.

Table 4.9         Criteria of Non-carcinogenic Health Impact Arising from Long Term COC Exposure and Background Concentration

COC

Sb

As

Cd

Cr (VI)

Co

Cu

Dioxins

HCl

HF

Pb^(1)

Mn

Hg

Ni

Tl

V

Criteria Adopted / Derived (μg/m^3)

1

0.03

0.02

0.008

0.2

2

4E-05

20

14

1.5

0.15

1

0.05

1

0.1

Background Conc. (μg/m^3)

N/A

0.0063

0.00173

0.00018

N/A

0.168

6.5E-8

N/A

N/A

0.14

0.040

0.00020

0.0059

N/A

0.0074

Non-carcinogenic Health Impact Significant?

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

Note (1): Since the long term criteria for lead is based on the 3-month average HKAQO, a 3-month average background concentration of lead was thus conservatively estimated based on the annual average background concentration of lead with a general power law relationship in the form of C_3-month = C_Annual x (12 month / 3 month)^p, where C_3-month is the 3-month average concentration; C_Annual is the annual average concentration; and p is the power law exponent conservatively taken as 0.5.  In other words, C_3-month = C_Annual x 2.

Table 4.10       Cumulative Non-carcinogenic Health Impact Arising from Long Term COC Exposure (Near Field)

COC

ASR

Sb

As

Cd

Cr (VI)

Co

Cu

Dioxins

HCl

HF

Pb^(1)

Mn

Hg

Ni

Tl

V

Criteria Adopted / Derived (μg/m^3)

-

1

0.03

0.02

0.008

0.2

2

4E-05

20

14

1.5

0.15

1

0.05

1

0.1

Long Term Average Conc. (μg/m^3)

A1

2.30E-04

6.52E-03

1.86E-03

6.90E-04

2.10E-04

1.69E-01

6.52E-08

4.39E-02

6.80E-04

1.43E-01

4.04E-02

3.40E-04

6.36E-03

1.30E-04

7.91E-03

A2

1.34E-03

7.62E-03

1.97E-03

1.74E-03

1.31E-03

1.70E-01

6.54E-08

1.24E-01

2.92E-03

1.45E-01

4.15E-02

4.40E-04

7.43E-03

2.40E-04

8.96E-03

A3

1.31E-03

7.59E-03

1.97E-03

1.71E-03

1.28E-03

1.70E-01

6.54E-08

1.49E-01

2.93E-03

1.45E-01

4.14E-02

4.40E-04

7.42E-03

2.40E-04

8.93E-03

A4

7.80E-04

7.06E-03

1.91E-03

1.18E-03

7.40E-04

1.69E-01

6.53E-08

1.02E-01

1.92E-03

1.44E-01

4.09E-02

3.80E-04

6.90E-03

1.80E-04

8.40E-03

A5

1.12E-03

7.39E-03

1.99E-03

1.61E-03

1.08E-03

1.70E-01

6.54E-08

1.34E-01

2.56E-03

1.46E-01

4.14E-02

4.60E-04

7.30E-03

2.60E-04

8.83E-03

A6

6.90E-04

6.95E-03

1.95E-03

1.15E-03

6.30E-04

1.69E-01

6.54E-08

1.71E-01

1.94E-03

1.45E-01

4.10E-02

4.20E-04

6.89E-03

2.20E-04

8.37E-03

A7

8.00E-05

6.36E-03

1.86E-03

5.40E-04

4.00E-05

1.68E-01

6.52E-08

1.46E-01

4.90E-04

1.43E-01

4.02E-02

3.30E-04

6.24E-03

1.30E-04

7.76E-03

A8

1.06E-03

7.26E-03

2.00E-03

1.43E-03

9.00E-04

1.70E-01

6.59E-08

1.12E-01

3.51E-03

1.48E-01

4.13E-02

4.70E-04

7.36E-03

2.70E-04

8.65E-03

A9

3.10E-04

6.59E-03

1.87E-03

7.20E-04

2.80E-04

1.69E-01

6.52E-08

6.79E-02

8.80E-04

1.43E-01

4.05E-02

3.40E-04

6.42E-03

1.40E-04

7.94E-03

A22

5.50E-04

6.81E-03

1.90E-03

9.61E-04

4.80E-04

1.69E-01

6.54E-08

1.84E-01

1.76E-03

1.45E-01

4.07E-02

3.80E-04

6.73E-03

1.70E-04

8.18E-03

Non-carcinogenic Health Impact Significant?

-

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

Note (1): Since the long term criteria for lead is based on the 3-month average HKAQO, the long term average concentration of lead in 3-month averages was thus conservatively estimated based on the predicted annual average concentration of lead with a general power law relationship in the form of C_3-month = C_Annual x (12 month / 3 month)^p, where C_3-month is the 3-month average concentration; C_Annual is the annual average concentration; and p is the power law exponent conservatively taken as 0.5.  In other words, C_3-month = C_Annual x 2.

Table 4.11                            Cumulative Non-carcinogenic Health Impact Arising from Long Term COC Exposure (Far Field)

COC

ASR

Sb

As

Cd

Cr (VI)

Co

Cu

Dioxins

HCl

HF

Pb^(1)

Mn

Hg

Ni

Tl

V

Criteria Adopted / Derived (μg/m^3)

-

1

0.03

0.02

0.008

0.2

2

4E-05

20

14

1.5

0.15

1

0.05

1

0.1

Long Term Average Conc. (μg/m^3)

A10

1.26E-04

6.43E-03

1.85E-03

5.76E-04

1.16E-04

1.68E-01

6.51E-08

3.24E-02

3.82E-04

1.43E-01

4.04E-02

3.22E-04

6.25E-03

1.22E-04

7.80E-03

A11

4.16E-04

6.60E-03

1.93E-03

7.58E-04

2.26E-04

1.69E-01

6.59E-08

1.52E-01

2.51E-03

1.47E-01

4.05E-02

4.03E-04

6.75E-03

2.03E-04

7.98E-03

A12

1.83E-04

6.46E-03

1.95E-03

8.58E-04

1.47E-04

1.69E-01

6.53E-08

7.81E-02

7.79E-04

1.45E-01

4.05E-02

4.25E-04

6.48E-03

2.25E-04

8.08E-03

A13

2.82E-04

6.48E-03

3.37E-03

4.43E-03

1.22E-04

1.73E-01

6.58E-08

8.89E-02

1.96E-03

1.74E-01

4.30E-02

1.84E-03

9.20E-03

1.64E-03

1.17E-02

A14

3.71E-04

6.49E-03

2.32E-03

1.68E-03

8.17E-05

1.71E-01

6.64E-08

5.60E-02

3.28E-03

1.56E-01

4.08E-02

7.98E-04

7.52E-03

5.88E-04

8.90E-03

A15

3.63E-04

6.50E-03

2.21E-03

1.39E-03

9.25E-05

1.70E-01

6.63E-08

4.61E-02

3.14E-03

1.54E-01

4.07E-02

6.89E-04

7.30E-03

4.79E-04

8.61E-03

A16

6.40E-04

6.62E-03

3.03E-03

3.18E-03

1.10E-04

1.73E-01

6.75E-08

9.61E-02

6.01E-03

1.73E-01

4.30E-02

1.52E-03

9.10E-03

1.30E-03

1.04E-02

A17

3.19E-03

7.62E-03

2.78E-03

1.27E-03

1.22E-04

1.81E-01

7.95E-08

3.34E-01

3.35E-02

2.06E-01

4.17E-02

1.32E-03

1.28E-02

1.05E-03

8.46E-03

A18

5.91E-04

6.61E-03

1.84E-03

3.25E-04

1.31E-04

1.70E-01

6.72E-08

9.25E-02

5.24E-03

1.49E-01

4.02E-02

3.23E-04

6.95E-03

1.13E-04

7.54E-03

A19

5.12E-04

6.59E-03

1.84E-03

3.66E-04

1.52E-04

1.70E-01

6.67E-08

9.96E-02

4.20E-03

1.47E-01

4.03E-02

3.15E-04

6.78E-03

1.05E-04

7.58E-03

A20

7.14E-04

6.65E-03

1.90E-03

3.59E-04

1.24E-04

1.70E-01

6.78E-08

1.15E-01

6.67E-03

1.52E-01

4.04E-02

3.82E-04

7.23E-03

1.72E-04

7.57E-03

A21

4.25E-04

6.59E-03

1.89E-03

6.27E-04

1.95E-04

1.69E-01

6.61E-08

1.27E-01

2.85E-03

1.47E-01

4.05E-02

3.70E-04

6.73E-03

1.60E-04

7.85E-03

A23

8.67E-04

6.72E-03

1.91E-03

3.44E-04

1.27E-04

1.71E-01

6.85E-08

1.38E-01

8.23E-03

1.55E-01

4.04E-02

4.03E-04

7.52E-03

1.83E-04

7.56E-03

A24

2.23E-04

6.43E-03

2.26E-03

1.55E-03

7.56E-05

1.70E-01

6.57E-08

7.46E-02

1.81E-03

1.52E-01

4.09E-02

7.28E-04

7.07E-03

5.28E-04

8.77E-03

A25

1.65E-04

6.41E-03

2.50E-03

2.21E-03

7.92E-05

1.70E-01

6.54E-08

2.20E-02

1.15E-03

1.56E-01

4.14E-02

9.68E-04

7.46E-03

7.68E-04

9.43E-03

A26

2.18E-04

6.44E-03

2.47E-03

2.19E-03

8.19E-05

1.70E-01

6.57E-08

7.50E-02

1.70E-03

1.56E-01

4.10E-02

9.38E-04

7.48E-03

7.38E-04

9.41E-03

A27

2.21E-04

6.43E-03

2.13E-03

1.28E-03

8.63E-05

1.69E-01

6.57E-08

5.36E-02

1.67E-03

1.49E-01

4.05E-02

5.99E-04

6.84E-03

3.99E-04

8.50E-03

A28

1.54E-04

6.41E-03

1.99E-03

8.74E-04

8.39E-05

1.69E-01

6.53E-08

2.60E-02

8.78E-04

1.46E-01

4.05E-02

4.58E-04

6.54E-03

2.58E-04

8.09E-03

A29

1.66E-04

6.42E-03

2.53E-03

2.24E-03

9.19E-05

1.70E-01

6.54E-08

3.36E-02

1.01E-03

1.56E-01

4.16E-02

9.99E-04

7.46E-03

7.99E-04

9.46E-03

A30

2.53E-04

6.45E-03

2.12E-03

1.30E-03

9.95E-05

1.69E-01

6.58E-08

4.97E-02

1.91E-03

1.49E-01

4.04E-02

5.90E-04

6.84E-03

3.90E-04

8.52E-03

A31

2.16E-04

6.45E-03

1.97E-03

8.85E-04

1.04E-04

1.69E-01

6.56E-08

7.53E-02

1.46E-03

1.46E-01

4.04E-02

4.40E-04

6.55E-03

2.40E-04

8.10E-03

A32

3.26E-04

6.48E-03

2.42E-03

1.84E-03

8.87E-05

1.70E-01

6.61E-08

3.36E-02

2.77E-03

1.56E-01

4.16E-02

8.89E-04

7.48E-03

6.89E-04

9.06E-03

Non- carcinogenic Health Impact Significant?

-

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

Note (1): Since the long term criteria for lead is based on the 3-month average HKAQO, the long term average concentration of lead in 3-month averages was thus conservatively estimated based on the predicted annual average concentration of lead with a general power law relationship in the form of C_3-month = C_Annual x (12 month / 3 month)^p, where C_3-month is the 3-month average concentration; C_Annual is the annual average concentration; and p is the power law exponent conservatively taken as 0.5.  In other words, C_3-month = C_Annual x 2.

Table 4.12       Criteria for Non-carcinogenic Health Impact Arising from Acute COC Exposure and Background Concentration

COC

Sb

As

CO

Cd

Cr (VI)

Co

Cu

HCl

HF

Pb

Mn

Hg

Ni

Tl

V

Criteria Adopted / Derived (μg/m^3)

150

3

30000

3

3

300

100

2100

240

15

300

1.8

6

30

15

Background Conc. (μg/m^3)

N/A

0.0063

932

0.00173

0.00018

N/A

0.168

N/A

N/A

0.070

0.040

0.00020

0.0059

N/A

0.0074

Non-carcinogenic Health Impact Significant?

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

Table 4.13       Cumulative Non-carcinogenic Health Impact Arising from Acute COC Exposure (Near Field)

COC

ASR

Sb

As

CO

Cd

Cr (VI)

Co

Cu

HCl

HF

Pb

Mn

Hg

Ni

Tl

V

Criteria Adopted / Derived (μg/m^3)

-

150

3

30000

3

3

300

100

2100

240

15

300

1.8

6

30

15

Hourly Average Conc. (μg/m^3)

A1

3.08E-02

3.71E-02

9.86E+02

4.80E-03

3.66E-02

3.08E-02

2.06E-01

4.77E+00

2.46E-01

2.06E-01

7.08E-02

3.27E-03

3.67E-02

3.07E-03

4.38E-02

A2

6.37E-02

7.00E-02

9.61E+02

8.10E-03

6.39E-02

6.37E-02

2.32E-01

8.66E+00

5.10E-01

1.34E-01

1.04E-01

6.57E-03

6.96E-02

6.37E-03

7.11E-02

A3

5.57E-02

6.20E-02

9.62E+02

7.30E-03

5.59E-02

5.57E-02

2.24E-01

8.84E+00

4.46E-01

1.26E-01

9.57E-02

5.77E-03

6.16E-02

5.57E-03

6.31E-02

A4

9.60E-02

1.02E-01

9.63E+02

1.13E-02

9.62E-02

9.60E-02

2.64E-01

1.20E+01

7.68E-01

1.66E-01

1.36E-01

9.80E-03

1.02E-01

9.60E-03

1.03E-01

A5

6.33E-02

6.96E-02

9.58E+02

8.06E-03

6.35E-02

6.33E-02

2.31E-01

8.48E+00

5.07E-01

1.33E-01

1.03E-01

6.53E-03

6.92E-02

6.33E-03

7.07E-02

A6

6.96E-02

7.59E-02

9.56E+02

8.69E-03

6.98E-02

6.96E-02

2.38E-01

8.70E+00

5.57E-01

1.40E-01

1.10E-01

7.16E-03

7.55E-02

6.96E-03

7.70E-02

A7

2.18E-02

2.81E-02

9.91E+02

3.91E-03

2.20E-02

2.18E-02

1.90E-01

1.37E+01

1.74E-01

9.18E-02

6.18E-02

2.38E-03

2.77E-02

2.18E-03

2.92E-02

A8

6.31E-02

6.94E-02

9.53E+02

8.04E-03

6.33E-02

6.31E-02

2.31E-01

7.82E+00

5.05E-01

1.33E-01

1.03E-01

6.51E-03

6.90E-02

6.31E-03

7.05E-02

A9

3.49E-02

4.12E-02

1.01E+03

1.14E-02

3.51E-02

3.49E-02

2.03E-01

9.11E+00

2.80E-01

1.70E-01

7.49E-02

9.89E-03

4.08E-02

9.68E-03

4.23E-02

A22

7.99E-02

8.62E-02

9.60E+02

9.72E-03

8.01E-02

7.99E-02

2.48E-01

1.22E+01

6.39E-01

1.50E-01

1.20E-01

8.19E-03

8.58E-02

7.99E-03

8.73E-02

Non- Carcinogenic Health Impact Significant?

-

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

Table 4.14       Cumulative Non-carcinogenic Health Impact Arising from Acute COC Exposure (Far Field)

COC

ASR

Sb

As

CO

Cd

Cr

Co

Cu

HCl

HF

Pb

Mn

Hg

Ni

Tl

V

Criteria Adopted / Derived (μg/m^3)

-

150

3

30000

3

3

300

100

2100

240

15

300

1.8

6

30

15

Hourly Average Conc. (μg/m^3)

A10

5.99E-02

6.62E-02

1.14E+03

1.38E-02

6.01E-02

5.99E-02

2.28E-01

7.19E+00

4.79E-01

2.03E-01

9.99E-02

1.23E-02

6.58E-02

1.20E-02

6.73E-02

A11

5.13E-02

5.18E-02

1.12E+03

4.74E-02

1.29E-01

4.55E-02

3.72E-01

7.16E+00

5.55E-01

5.56E-01

8.55E-02

4.59E-02

1.07E-01

4.57E-02

1.36E-01

A12

3.37E-02

4.00E-02

1.19E+03

1.78E-02

4.91E-02

3.37E-02

2.30E-01

4.49E+01

2.70E-01

2.33E-01

8.21E-02

1.63E-02

4.13E-02

1.61E-02

5.63E-02

A13

9.55E-02

1.02E-01

2.81E+03

1.18E-01

2.58E-01

9.55E-02

5.83E-01

2.80E+01

7.64E-01

1.53E+00

3.46E-01

1.18E-01

2.84E-01

1.16E-01

2.66E-01

A14

1.20E-01

5.30E-02

1.31E+03

3.38E-02

9.39E-02

1.24E-02

6.44E-01

1.82E+01

1.30E+00

1.21E+00

1.07E-01

3.23E-02

2.42E-01

3.21E-02

1.01E-01

A15

2.34E-02

2.28E-02

1.17E+03

2.41E-02

6.32E-02

1.65E-02

2.58E-01

7.75E+00

2.48E-01

3.37E-01

7.83E-02

2.26E-02

5.98E-02

2.24E-02

7.04E-02

A16

8.98E-02

4.14E-02

1.90E+03

4.53E-02

1.23E-01

3.33E-02

5.40E-01

1.73E+01

9.72E-01

1.08E+00

1.98E-01

4.39E-02

2.08E-01

4.36E-02

1.30E-01

A17

3.00E-01

1.24E-01

1.45E+03

6.03E-02

1.08E-01

6.69E-02

1.36E+00

2.60E+01

3.25E+00

2.92E+00

1.24E-01

6.56E-02

5.99E-01

5.86E-02

1.15E-01

A18

6.35E-02

3.12E-02

9.51E+02

1.41E-02

2.19E-02

2.17E-02

4.20E-01

5.51E+00

6.87E-01

6.71E-01

6.17E-02

1.42E-02

1.31E-01

1.24E-02

2.91E-02

A19

3.97E-02

3.29E-02

1.14E+03

3.06E-02

7.96E-02

2.66E-02

3.24E-01

3.57E+00

4.29E-01

4.42E-01

7.60E-02

2.91E-02

8.38E-02

2.88E-02

8.68E-02

A20

5.70E-02

3.30E-02

1.14E+03

1.29E-02

2.69E-02

2.67E-02

3.95E-01

6.09E+00

6.17E-01

6.11E-01

7.35E-02

1.26E-02

1.19E-01

1.11E-02

3.41E-02

A21

4.28E-02

4.91E-02

1.17E+03

5.99E-02

1.65E-01

4.28E-02

3.35E-01

6.19E+00

3.42E-01

6.69E-01

8.28E-02

5.84E-02

1.20E-01

5.82E-02

1.72E-01

A23

7.22E-02

3.46E-02

1.13E+03

1.58E-02

2.31E-02

2.29E-02

4.54E-01

7.14E+00

7.81E-01

7.53E-01

7.47E-02

1.60E-02

1.48E-01

1.41E-02

3.03E-02

A24

5.56E-02

2.80E-02

1.94E+03

2.76E-02

6.50E-02

2.15E-02

3.89E-01

4.36E+01

6.02E-01

6.55E-01

2.03E-01

2.65E-02

1.24E-01

2.58E-02

7.22E-02

A25

1.71E-02

2.34E-02

3.16E+03

1.01E-01

2.21E-01

1.71E-02

3.50E-01

3.65E+00

1.37E-01

9.69E-01

4.03E-01

9.97E-02

1.66E-01

9.95E-02

2.28E-01

A26

2.50E-02

3.13E-02

1.98E+03

7.50E-02

1.84E-01

2.50E-02

3.33E-01

4.38E+01

2.37E-01

7.67E-01

2.10E-01

7.35E-02

1.34E-01

7.33E-02

1.91E-01

A27

2.58E-02

2.44E-02

1.13E+03

2.15E-02

5.73E-02

1.81E-02

2.56E-01

1.45E+01

2.64E-01

2.87E-01

7.45E-02

2.00E-02

5.42E-02

1.98E-02

6.45E-02

A28

2.43E-02

2.32E-02

1.16E+03

2.36E-02

6.16E-02

1.69E-02

2.54E-01

6.87E+00

2.53E-01

2.99E-01

7.74E-02

2.21E-02

5.08E-02

2.19E-02

6.88E-02

A29

3.00E-02

2.72E-02

2.84E+03

1.03E-01

2.40E-01

2.09E-02

3.71E-01

1.14E+01

3.15E-01

9.93E-01

3.64E-01

1.01E-01

1.82E-01

1.01E-01

2.47E-01

A30

1.06E-01

4.76E-02

1.10E+03

3.29E-02

8.75E-02

2.26E-02

5.88E-01

1.04E+01

1.15E+00

1.07E+00

6.85E-02

3.13E-02

2.15E-01

3.11E-02

9.48E-02

A31

6.94E-02

4.73E-02

1.14E+03

1.64E-02

4.14E-02

4.10E-02

4.44E-01

4.48E+01

7.51E-01

7.31E-01

8.10E-02

1.58E-02

1.43E-01

1.47E-02

4.86E-02

A32

2.28E-02

2.59E-02

3.10E+03

4.75E-02

9.17E-02

1.96E-02

2.68E-01

4.68E+00

2.47E-01

4.14E-01

3.93E-01

4.60E-02

7.53E-02

4.58E-02

9.89E-02

Non- carcinogenic Health Impact Significant?

-

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

4.2.7 Uncertainty of the Assessment

4.2.7.1 The HHRA is a complex process, requiring the integration of the followings:

l    Release of COCs into the environment;

l    Transport of the COCs by air dispersion, in a variety of different and variable environments;

l    Potential for adverse health effects in human, as extrapolated from animal studies; and

l    Probability of adverse effects in a human population that is highly variable genetically, and in age, activity level and lifestyle.

4.2.7.2 Uncertainty can be introduced in the assessment at many steps of the process.  The following paragraphs discuss the uncertainties associated with each stage of the assessment.

Hazard Identification

4.2.7.3 COCs are identified based on the air pollutants listed in EPD’s BPM12/1.  This list of chemicals may not cover all the chemicals emitted from the stack of STF which could pose a threat to human health, which may underestimate the risk.  However, it is considered that although the COCs identified may not be exhaustive, it appeared sufficiently comprehensive for the purpose of the assessment because BPM12/1 serves the purpose to prevent the air pollutant emissions from incinerator stack from harming the environment and human health or creating nuisance. 

4.2.7.4 The adopted emission factors of COCs from STF stack for air quality modelling are based on the exhaust gas concentration limits stated in BPM12/1.  It is considered that this assumption would overestimate the risk because COC emission rate from STF would not reach the allowed maximum rate all the time.  Moreover, the emission factors for individual heavy metals (except Hg) are based on the “exhaust gas concentration for combined metal species”[3], this would further overestimate the risk.

Exposure Assessment

4.2.7.5 In this stage of the HHRA, air dispersion model is used to predict the COC dispersion in air and the COC concentrations at potential human receptors.  As computer models are simplifications of reality requiring exclusion of some variables that influence predictions, of which would introduce uncertainty in the prediction of COC concentration at potential human receptors and may in turn overestimate or underestimate the risk. 

4.2.7.6 Moreover, the air quality modelling results adopted for exposure assessment are modelled based on the worst case scenario which would not occur all the time.  This conservative approach in air quality modelling would overestimate the risk.

4.2.7.7 This HHRA only considers inhalation pathway as the major COC exposure pathway for calculation of exposure, which is consistent with the approach adopted in previous local studies.  Other exposure pathways such as dermal contact and incidental ingestion of soil are not considered, which may underestimate the risk.  However, the risk underestimation is considered insignificant because the exposure pathways not considered are expected to be minor for the potential human receptors. 

4.2.7.8 The characteristic parameter values for human receptors used in the HHRA are adopted from the default values suggested in USEPA (2005).  The values adopted may not precisely reflect the conditions of potential human receptors identified, which may overestimate or underestimate the risk.

Dose-response Assessment

4.2.7.9 The air quality benchmarks[4] adopted from agencies would introduce uncertainty to the HHRA.  These air quality benchmarks are used as single-point estimates throughout the analysis with uncertainty and variability associated with them.  Moreover, the arbitrary application of safety factor to occupational exposure limit for derivation of air quality benchmark for long term COC exposure is another source of uncertainty.  This uncertainty may overestimate or underestimate the risk.  However, it should be noted that much of the uncertainty and variability associated with the air quality benchmarks shall be accounted for in the process that the agencies setting verified benchmarks.    

Risk / Hazard Characterization

4.2.7.10 The risk for long term exposure of individual COC is characterized by comparing the predicted COC concentrations at potential human receptor with corresponding air quality standard.  This approach provides a simple comparison to characterize the risk but it does not consider the possible cumulative effects (additional, synergistic or antagonistic effect) of exposure to multiple COCs and introduce uncertainty to the risk assessment.  However, adoption of “Hazard Quotient” approach (another approach to characterize the non-carcinogenic effect of COC exposure), which could provide a mechanism to assess the cumulative impact of the exposure of multiple contaminants, would also introduce uncertainty to the assessment.

4.3 HHRA for Microbes from Dewatered Sewage Sludge

4.3.1 Overview

4.3.1.1 This section presents the assessment for the health risk associated with microbes from dewatered sewage sludge during their transportation, storage and handling in the STF operation. 

4.3.1.2 According to the EIA Study Brief, a literature search shall be carried out to determine the best approach for the risk assessment.  The results of the literature search revealed that qualitative approach was appropriate for the assessment, based on the following rationales:

l A high degree of uncertainty would be encountered when the health risk is to be quantified, due to lack of precise and comprehensive data;

l The degree of survival and transport of pathogens in the environment is limited; and

l Qualitative risk assessment is well recognized as appropriate methodology for microbial risk assessment and has been adopted for both local and overseas studies.

4.3.1.3 The health risk assessment for microbial emissions includes the following steps:

l Identification of the hazards associated with microbes during transportation, storage and handling of dewatered sewage sludge

l An assessment of the likelihood and consequences of exposure of microbes during transportation, storage and handling of dewatered sewage sludge

l A qualitative assessment of the likely level of risks associated with the identified hazards

l Identification and recommendation of means by which the potential risks could be further reduced

4.3.2 Risk Assessment Methodology

4.3.2.1 This section details the methodology of the risk assessment and presents the assessment results.  To facilitate the assessment, the whole process train of STF operation dealing with dewatered sewage sludge was categorized into 8 processes and each process was considered separately.  The 8 processes are listed as follows:

l Sludge collection

l Sludge transport

l Sludge reception and handling (at STF)

l Temporary storage of sludge (at STF)

l Sludge conveyance from temporary storage to incinerator unit (at STF)

l Sludge incineration (at STF)

l Wash down facilities (at STF)

l Maintenance and repair activities (at STF)

4.3.2.2 The hazard of concern for all the above processes is associated with the presence of infectious substances; other occupational hazards were not considered.

Hazard Identification

4.3.2.3 In this assessment, hazard is considered as “potential of exposure to disease-causing microbes from dewatered sewage sludge”.  Hazard and Operability (HAZOP) technique was applied for the hazard identification process in the assessment. 

4.3.2.4 HAZOP facilitates a team of workshop participants to systematically identify possible deviation from the design / operation intent (i.e. hazard) by applying a combination of property words and guidewords.  It is a common technique in hazard identification exercise.  

4.3.2.5 A HAZOP workshop was held and participated by the Consultants (design engineers and environmental specialists) for this risk assessment.  The property words and guidewords used are presented in Table 4.15.

Table 4.15       Property Words and Guidewords used in HAZOP Workshop

Property Word	Guideword
Amount	More / less / other / incorrect
Driver / operator	Error
Equipment	Down / failure / accident
Sealing	No, inadequate, inappropriate
Stowage / Storage	Incorrect / inadequate / inappropriate /error
Temperature	High / low
Timing / time	More / less / no / before / after
Drainage	No / blocked

Frequency Analysis

4.3.2.6 The occurrence frequency of the identified hazards was determined in the HAZOP workshop by discussion among the participants based on their knowledge on the design and operation of STF as well as their experience and professional judgment.  Existing / expected safeguards (i.e. risk control measures) were taken into consideration for the analysis of frequency.  The frequency of occurrence was assessed using the following categories:

l 1 – low likelihood

l 2 – medium likelihood

l 3 – high likelihood

Consequence Analysis

4.3.2.7 The consequence of the hazards was assessed using the following categories, which were derived from the classification of biological agents in the COSHH Regulations (i.e. Hazard Group):

l 1 – unlikely to cause human disease

l 2 – can cause human disease and may be a hazard to employees; it is unlikely to spread to the community and there is usually effective prophylaxis or treatment available

l 3 – can cause severe human disease and may be a serious hazard to employees; it may spread to the community but there is usually effective prophylaxis or treatment available

l 4 – causes severe human disease and is a serious hazard to employees; it is likely to spread to the community and there is usually no effective prophylaxis or treatment available

4.3.2.8 According to NIOSH (2002) and HSE (2004), no Hazard Group 4 pathogen but some Hazard Group 2 or 3 pathogens were considered as the pathogens of concern in sewage sludge.  Therefore, a consequence level of 3 was assigned for all identified hazards associated with dewatered sewage sludge exposure.

Risk Analysis and Evaluation

4.3.2.9 A simple 3 x 4 risk matrix was used to assess the likely risk levels for the identified hazards.  The risk matrix used is presented in Table 4.16.  

Table 4.16         Risk Matrix

		Hazard Consequence
		1	2	3	4
Hazard Likelihood	1 – Low	Low	Low	Medium	Medium
	2 – Medium	Low	Medium	Medium	High
	3 – High	Medium	Medium	High	High

4.3.2.10 As shown in Table 4.16 above, “low”, “medium” or “high” level of risk was categorized for each identified hazard under risk analysis.  The three levels of risk were categorized as follows:

l “Low” risk level – the risk of the hazard could be considered to be broadly acceptable.  In such cases, no further mitigation measures are considered necessary

l “Medium” risk level – the risk of the hazard could be considered to be tolerable, mitigation measures and/or safeguard measures can be provided to reduce the risk level to “As Low As Reasonably Practicable”

l “High” risk level – the risk of the hazard could be considered to be unacceptable.  Mitigation measures should be applied to reduce the risk level

Risk Mitigation

4.3.2.11 When the risk assessment result revealed that risk mitigation measures for particular hazards are necessary, risk mitigation measures would be identified and the residual level of risk will be analyzed.  

4.3.3 Risk Assessment Result

4.3.3.1 The results of the risk assessment are summarized in Table 4.17.  The detailed risk assessment worksheets are presented in Appendix 4.1. 

4.3.3.2 As presented in Table 4.17, 25 hazards associated with collection, transport, handling, incineration of dewatered sewage sludge and STF operations were identified.  With consideration of existing / expected safeguards, the risk levels of all the 25 hazards were analyzed to be medium, which can be considered to be tolerable.

Table 4.17       Summary of Risk Assessment Results

Process	No. of Identified Hazards in Each Risk Category
	Low	Medium	High
Sludge Collection	0	4	0
Sludge Transport	0	5	0
Sludge Reception and Handling	0	7	0
Temporary Sludge Storage	0	3	0
Sludge Conveyance from Temporary Storage Tank to Incinerator	0	1	0
Sludge Incineration	0	2	0
Wash Down Facilities	0	2	0
Maintenance and Repairing	0	1	0

4.3.3.3 Since the consequence of sewage sludge exposure was assigned to be 3 for all hazards, the means to reduce the risk level of identified hazards were to reduce the likelihood of hazard occurrence.  The existing / expected safeguards for most of the identified hazards reduce the likelihood of failure events (e.g. overfilling of container of transport vehicle / temporary storage tank) or sludge exposure by on-site cleaning and maintenance workers.  For hazards related to transport accident and equipment failure, their likelihoods of occurrence were considered to be low and further reduction of likelihood would not effectively reduce the risk level.  Hence, the risk levels of the identified hazards were considered to be “As Low As Reasonably Practicable”.

4.3.4 Conclusions and Recommendations

4.3.4.1 A health risk assessment for the microbes from dewatered sewage sludge associated with the STF operation has been undertaken.  In accordance with the EIA Study Brief, a literature search was conducted and the results revealed that a qualitative assessment approach was considered appropriate. 

4.3.4.2 Twenty five hazards concerning microbial emissions associated with collection, transport, handling, incineration of dewatered sewage sludge and STF operations were identified.  With consideration of existing / expected safeguards, the risk levels of all the 25 hazards were found to be tolerable and “As Low As Reasonably Practicable”. 

4.3.4.3 The following risk control measures (identified as existing / expected safeguards) should be maintained / implemented when STF is in operation to ensure the findings of the risk assessment remain valid:

Sludge collection 

l Apply good practice during unloading of dewatered sewage sludge to skip / container of transport vehicle

l The dewatered sewage sludge unloading process should be supervised by workers on-site and drivers

Sludge Transport

l The workers handling the dewatered sewage sludge spillage during transport in case of accident should wear personal protective equipment

Sludge Reception and Handling at STF

l Provide signage to assist driver to stop at appropriate unloading position

l Provide sufficient training to drivers for the dewatered sewage sludge transporting vehicles

l The on-site workers responsible for cleaning should wear personal protective equipment

l Vehicle cleaning system should be provided to clean the dewatered sewage sludge transporting vehicle before they leave the STF

l Monitor and control the traffic flow inside the reception hall of the STF

l Provide signage for clear indication of vehicle travelling route

l In case manual handling of dewatered sewage sludge is needed, the workers involved should wear personal protective equipment

Temporary Sludge Storage at STF

l Detection device / alarm should be installed to prevent overfilling of temporary sludge storage tank

l Monitor and control the dewatered sewage sludge unloading process

l The on-site workers responsible for cleaning should wear personal protective equipment

l A safety margin should be considered for the design capacity of STF

l Emergency plan should be established and implemented to handle the situation of incineration units being down

Sludge Incineration at STF

l Monitoring and control system should be installed to monitor and control the performance of incineration process

l In case handling of incomplete combusted dewatered sewage sludge is needed, the workers involved should wear personal protective equipment

Wash Down Facilities at STF

l The on-site workers responsible for cleaning should wear personal protective equipment

l Frequent and sufficient maintenance should be provided for the drainage system of STF 

l Multiple outlets in drainage system should be designed and provided to reduce the likelihood of drainage blockage 

Maintenance and Repairing at STF

l Maintenance workers should wear personal protective equipment 

4.4 HHRA for Radon Emission from Pulverized Fly Ash

4.4.1 Introduction

4.4.1.1 As the proposed STF would be built on the eastern part of the existing ash lagoon at Tsang Tsui near Nim Wan, the potential health risk induced by radon emissions associated with PFA arising from the construction and operation of the STF is required to be evaluated.

4.4.1.2 According to the EIA Study Brief, a literature search shall be carried out to determine the best approach for the risk assessment.  The findings of the literature search indicated the following:

l Health risks for radon emission due to construction and operation activities of the STF would be insignificant;

l Radiation exposure to the staff in the STF from the radon flux out of the ground filled by PFA may be increased but would not be of great significance with implementation of proper mitigation measures; and

l A review of radon risk should be undertaken, based on the confirmed construction method.

4.4.1.3 This section presents the literature review and assessment for the health risk associated with radon emissions from PFA during the construction and operation phases of the STF.

4.4.2 Health Hazard of Radon

4.4.2.1 Radon-222 exists as a naturally occurring radioactive inert gas with a half-life 3.82 days and is a decay product of radium-226, which is present in geological materials (rocks, soil, etc.) and concrete at natural levels.

4.4.2.2 Radon naturally decays into a series of radioisotopes as illustrated in the “radon progeny” in Figure 4.1.  Each radioactive element on the list gives off either alpha or beta radiation, and sometimes gamma radiation too – thereby transforming itself into the next element on the list.

4.4.2.3 Radon is an indoor air quality concern because the radium family is present in most building materials.  The presence of these radioisotopes in the building materials causes external exposure to the people that occupy the building. Inhalation of gaseous radon as well as its short-lived progeny also leads to internal exposure of the respiratory tract to alpha particles.

4.4.2.4 In living lung tissue, if the DNA in one of the cells adjacent to an inhaled radioactive particle is damaged by the emitted radiation, it may later become a cancer cell that may spread through the lung, perhaps causing death of the individual.

4.4.2.5 The Relative Risk Model (Yu et al.), which takes into account various factors, such as age and sex, has been used to estimate the excess lung cancer deaths due to radon.  It has been found that, around the year 1988, about 300 (about 13%) of the lung cancer deaths each year are attributable to radon in Hong Kong.

4.4.2.6 In addition, chronic exposure of human beings to low doses of ionizing radiation can cause health damages which may appear 5 – 30 years after the exposure.  The most critical damage which can result from such exposure is an increase in the probability of contracting malignant diseases by the person who was exposed.

4.4.2.7 It is believed that the radon health risk also increases with the dose, and the probability of the appearance of damage is greater when the exposure starts at a younger age.

4.4.3 Radon Characteristics of the Project

Radon Sources

4.4.3.2 Radon gas may be liberated from PFA contained in the ash lagoon.  PFA is a by-product of the combustion process of an electric utility plant.  Coal contains uranium-238, which is the parent element of the uranium series.  After the combustion process, the concentration of the radioactive content in the PFA may increase and consequently, the radon concentration as well as its health risk potential may also increase.

4.4.3.3 Suspended particulate, including fine dust from PFA, may also be an incremental source of radiation.  Re-suspension of materials from surfaces is affected by the nature of the surface and the strength of the wind or other disturbing agents.

4.4.3.4 As mentioned in Section 4.4.2, radon also occurs naturally as an inert gas. Cautiously speaking, the worldwide, population-averaged radon concentration is estimated to be 10 Bq/m³ in an ambient outdoors condition.  However, this content is not considered in the assessment but only involved in estimation of the total annual dose equivalent in Green’s Study as illustrated in Section 4.4.4.

Pathway Exposure

4.4.3.5 Radon gas will emanate from the PFA to the air above the ash lagoon.  Cracks on the walls and floors would also facilitate the ingress of radon gas from the PFA into the building structures located on top of the PFA.  Radon flux from the PFA mainly depends on the emanation power of the PFA.

4.4.3.6 The pathway exposure also includes inhalation of suspended material containing radionuclide.

Target Sensitive Receivers

4.4.3.7 It is anticipated that the workers during the construction and operation stages would be exposed to higher radon health risk.  Particularly, the workers in an indoors environment or confined space could be affected by elevated radon concentration.

4.4.3.8 Regarding truck drivers, who would visit the Project site occasionally, there may also be a risk potential from radon.  However, as the risk level is dependent on the duration of exposure, it is considered that the target sensitivity should be lower than that of the workers on site.

4.4.4 Risk Assessment of Radon Emission Associated with PFA

4.4.4.1 As addressed in the literature research, the health risk due to radon emission due to construction and operation of STF is considered insignificant.  In this section, the results of these previous relevant studies are discussed to demonstrate an insignificant health risk.  Alpha particles and gamma ray dose are both taken into account in the evaluation of annual effective dose equivalents.

4.4.4.2 A study on radiological significance of the utilization and disposal of coal ash from power stations was conducted by Dr. B M R Green for Central Electricity Generating Board in 1986.

4.4.4.3 The objectives of the study were to assess the radiological significance of utilization of PFA as building materials and activities of workers and the general public on disposal sites, under both indoor and outdoor environment.  The significance was calculated on the basis of actual field study, laboratory study and mathematical models.

4.4.4.4 Field measurements were taken at three coal ash disposal sites in the United Kingdom (UK).  Radionuclide content, porosity, radon emanating fraction and exhalation rates of building blocks containing PFA were also analyzed. Mathematical models were used to estimate the exposure to gamma-ray dose rates and radon concentrations under the tested conditions:-

l Exposures from building materials; and

l Exposures from disposal sites under outdoors and indoors conditions.

4.4.4.5 From the field studies, it was found that there is an increase of radionuclide content from coal to PFA.  The result agrees with that from the assessment conducted by EPD and Royal Observatory (RO) in co-operation with the China Light & Power (CLP) in 1989.  The specific activity of samples of PFA, FBA (fuel bottom ash) and coal from the Castle Peak Power Stations was assessed.  The results have been extracted and shown in Table 4.18 after conversion to radium equivalent activities.  The data indicate an increased activity from unburned coal, FBA to PFA.

4.4.4.6 A number of observations were noted when predicting flux for various thicknesses of PFA and of soil cover in the field studies.  It was noted that increasing the thickness of the PFA layer beyond 5 m makes little impact on the surface radon flux.  The flux would be reduced by a factor of two if 30 cm of soil cover is provided on top of the PFA.

Table 4.18       Radium Equivalent Activities of PFA, FBA and Coal from the Castle Peak Power Station

Coal Source	Date of Sample Collection	Radium equivalent activity (Bq/kg)
		Coal	PFA	FBA
Columbia	22/02/89		233	255
Australia	22/02/89		373	347
Australia	02/03/89		532	163
South Africa	07/03/89		407	343
South Africa	08/03/89
South Africa	10/03/89	72	423	382
South Africa	15/03/89	66	443	335
Australia	19/03/89	27	211	197
Sampled by RO	1987		377^a
Source not specified	1987		378^a

Remark:  ^a Data from RO

4.4.4.7 Radon concentration under indoor and outdoor environment above an ash lagoon is estimated by mathematical models in Green’s Study.  As expected, the radon level and associated effective dose equivalent under outdoor condition is of low significant level.  The contribution from the PFA is calculated to be 1 Bqm^-3 and it may reduce to less than 0.5 Bqm^-3 if there is a soil cover of 50cm over the PFA.

4.4.4.8 Regarding an indoors environment, the radon concentration inside a reference all-brick dwelling built on an ash disposal site was estimated.  Two scenarios were considered: on ash with a covering of 50cm of soil and on ash without soil cover. It was found that the radon concentration in a dwelling built on an uncovered ash disposal site was calculated to be 28 Bqm^-3 and this value reduces to 13 Bqm^-3 if the ash is covered with 50cm of soil.  As a result, the annual effective dose equivalent to an occupant of the all-brick house on a covered ash disposal site was calculated to be 360μSv and this value increased to 780μSv if the ash is uncovered. The study also provided the corresponding values for heavy and light block houses on covered and uncovered ash disposal sites.

4.4.4.9 A mass-loading approach was used to predict the airborne activity levels due to dust particle suspension.  It was assumed that particulates in air had the same activity per unit mass as the surface material.  Besides, a dust loading of 100μgm^-3 over a PFA disposal site and an annual intake of dust of about 0.84g was assumed.  The committed effective dose from the annual intake of thorium, uranium and their long lived decay products was calculated to be 35μSv.

4.4.4.10 Table 4.19 provides the summary of the estimations of the effective dose equivalents under the above conditions in the study.

Table 4.19       Summary of Estimates of Annual Effective Dose Equivalents

Situation	Normal Ground			PFA disposal site 50cm soil cover			PFA disposal site no soil cover
	From g	From Rn	Total	From g	From Rn	Total	From g	From Rn	Total
Indoors
All-brick dwelling	0.740	0.260	1.000	0.750	0.360	1.110	0.760	0.780	1.540
Heavy block dwelling	0.700	0.290	0.990	0.710	0.400	1.110	0.720	0.820	1.540
Light block dwelling	0.530	0.340	0.870	0.540	0.440	0.980	0.560	0.860	1.420
Outdoors
Workers such as farm or disposal site labour (2000 hrs in a year)	0.056	0.057	0.113	0.070	0.060	0.130	0.130	0.060	0.190
Members of the public (500 hrs in a year)	0.014	0.007	0.021	0.018	0.008	0.026	N/A	N/A	N/A
Inhalation of Re-suspended Dust
(8,760 hrs in a year)			0.011			-			0.035

Note: Estimated Values (including values from gamma ray dose and radon) were rounded to two significant figures

            N/A: Not applicable

            All units in mSv

4.4.4.11 The estimation indicates that there is no significant radiological hazard to workers working out of doors or near either restored or working ash disposal sites.  The annual effective dose equivalent to a worker spending 2000 hours outdoors on an ash filled lagoon is about 0.19mSv and is not of great radiological significance level when compared with an annual limit of 1 mSv for general public suggested by the International Commission on Radiological Protection (ICRP).  Since the risk imposed on workers with direct radon exposure is not significant and that there will be no off-site disposal of PFA under this Project, the risk on off-site air sensitive receivers will also be insignificant as well. 

4.4.4.12 It was found that there is a potential increase in the radiation exposure of occupants in dwellings built over ash disposal sites from increased radon flux out of the ground.  The annual effective dose equivalent induced by radon in an indoors environment on an ash disposal site with 50cm soil cover is similar to that on a normal area but there is an increase on an uncovered ash field.  Nevertheless, the annual effective dose equivalent of about 1.5mSv in an indoors environment on an uncovered ash field, which includes contribution from gamma ray dose and radon concentration.  1.5mSv is not of great radiological significance level when compared with 10mSv, the exposure limit for indoor radon in dwellings and workplaces with reference to International Commission on Radiological Protection (ICRP).  As such, the staff of the future STF should not be exposed to a significant level of health risk due to radon.

4.4.4.13 There may be some differences in the working habits, ambient radon levels and radiological characteristics of PFA in the ash lagoon of the Project from the study cases in the reviewed literature.  However, it is anticipated that these differences should hardly elevate the health hazard to an unacceptable level.

4.4.5 Recommended Measures to Control Radon Health Risk

4.4.5.1 As discussed in the health risk assessment conducted by Green, there is no significant radiological hazard to the workers at the proposed STF on an ash lagoon during construction and operation periods.  However, under the “As Low as Reasonably Achievable” (ALARA Principle), recommended measures shall be considered during the design, construction and operation of the STF.

4.4.5.2 Prevention of radon influx from the PFA to the STF buildings is preferred.  A soil cover can be provided beneath the buildings on top of ash lagoon prior to construction works because it reduces the level of radon influx significantly.  Slab-on-grade can be an option on foundation design.  In addition, soil suction can also prevent radon from entering the building by drawing the radon from below the building and venting it through a pipe, or pipes, to the air above the building.

4.4.5.3 Sufficient ventilation of the interior of the STF buildings should be provided. Forced and natural ventilation should be introduced properly to enhance air exchange rate in the STF buildings.  Regarding basement areas, pressurization by using a fan to blow air into the basement areas from outdoors is suggested.  This would create enough pressure at the lowest level indoors to prevent radon from entering into the STF buildings.

4.4.5.4 Regular maintenance should be provided for the floor slabs and walls.  Cracks and other openings in the foundation should be properly sealed to reduce radon ingress. Sealing the cracks limits the flow of radon into the building thereby making other radon reduction techniques more effective and cost-efficient.  It also reduces the loss of conditioned air.

4.4.5.5 Prior to the occupation of the STF buildings and quarterly during the first year of operation of the STF, radon concentration shall be measured by professional persons in accordance with EPD’s ProPECC Note PN 1/99 Control of Radon Concentration in New Buildings Appendix 2, ”Protocol of Radon Measurement for Non-residential Building” to ensure the radon concentration is in compliance with the guidance value.

4.5 Conclusions

4.5.1.1 The cancer risk arising from exposure to carcinogenic contaminants of concern (COCs) associated with the emissions of STF is evaluated in this section.  In terms of lifetime individual excess cancer risks, the highest cancer risk arising from STF is predicted to be 1.51E-5 and is considered to be in “As Low As Reasonably Practicable” (ALARP) level.

4.5.1.2 Cumulative acute and long term non-carcinogenic health impact of the STF imposed to the worst impacted human receptors were assessed and compared with local and overseas guideline levels.  It was concluded that the levels of non-carcinogenic chemicals were found to be insignificant when compared to the adopted/derived reference levels.

4.5.1.3 Microbes from dewatered sewage sludge during their transportation, storage and handling in the STF operation were assessed.  Twenty-five hazards concerning microbial emissions associated with the STF operations were identified.  With consideration of existing/expected safeguards, the risk levels of all the 25 hazards were found to be tolerable and were at the level of “As Low As Reasonably Practicable”.

4.5.1.4 The potential health risk induced by radon emissions associated with PFA arising from the construction and operation was also evaluated.  The estimation indicated that there would be no significant radiological hazard to workers working outdoors in the STF or in the restored/operating ash lagoon area adjacent to the STF.  The annual effective dose equivalent to a worker spending 2000 hours outdoors on an ash filled lagoon would be about 0.19mSv, which is insignificant comparing to annual limit of 1 mSv for general public suggested by the International Commission on Radiological Protection (ICRP).  Since the risk imposed on workers with direct radon exposure is not significant and that there will be no off-site disposal of PFA under this Project, the risk on off-site air sensitive receivers will also be insignificant as well.  From various literature researches, the radon health risk for construction and operation of the proposed STF would be negligible.

4.6 Reference

AIHA (2005).  Current AIHA ERPGs (2005).  Available online: www.aiha.org/committees/documents/erpglevels.pdf.

California EPA (1999).  Air Toxics Hot Spots Program Risk Assessment Guidelines.  Part 1 – The Determination of Acute Reference Exposure Levels for Airborne Toxicants.

DoE.  Revision 21 of AEGLs, ERPGs and TEELs for Chemicals of Concern.  Available online: http://tis-hq.eh.doe.gov/web/chem_safety/teel.html.

EPD (2001).  A Guidance Note on the Best Practicable Means for Incinerators (Municipal Waste Incineration). BPM12/1.

ERM (2001).  Preliminary Project Feasibility Study for Sludge Treatment Facilities: Preliminary Environmental Review.

ERM (2003).  Feasibility Study of Animal Carcass Treatment Facilities: EIA Report (Agreement No. CE 68/2002).

HSE (2002).  EH40/2002 Occupational Exposure Limits 2002.

HSE (2004).  The Approved List of Biological Agents.

MWH (2003).  Additional Study of Waste-to-Energy Facilities (WEF) – EIA Report (Agreement No. CE 23/2002).

NIOSH (2002).  Guidance for Controlling Potential Risks to Workers Exposed to Class B Biosolids.

OEHHA (2005a).  All Chronic Reference Exposure Levels Adopted by OEHHA.  Available online: www.oehha.ca.gov/air/chronic_rels/AllChrels.html

OEHHA (2005b).  Toxicity Criteria Database.  Available online: www.oehha.ca.gov/risk/chemicalDB/index.asp.

USEPA.  Acute Exposure Guideline Levels (AEGLs).  Available online: www.epa.gov/oppt/aegl/chemlist.htm.

USEPA (2005).  Human Health Risk Assessment Protocol for Hazardous Waste Combustion Facilities – Final.

USEPA.  Integrated Risk Information System (IRIS) Database.  Available online: www.epa.gov/iris.

WHO (2000).  Air Quality Guidelines for Europe, 2^nd edition.

Green, B.M.R. (1986).  Radiological Significance of the Utilization and Disposal of Coal Fly Ash from Power Stations Report for Central Electricity Generating Board. National Radiological Protection Board, UK.

Yu, K.N., Young, E.C.M. and Stokes, M.J (1988).  The Radon-induced Lung Cancer Mortality in Hong Kong Deduced from a Relative Risk Model.

EPD (1999) ProPECC Note PN 1/99 Control of Radon Concentration in New Buildings

Binnie Consultants Limited (1990).  The Environmental Aspects of Fuel Ash Utilization.

CDM (2001), Feasibility Study of Waste-to-Energy Facilities – EIA (Ha Pak Nai) (Agreement No. CE97/96)

International Commission on Radiological Protection (IRCP) (2007), IRCP Recommendation (Publication 103)

---

[1] ERM (2001); ERM (2003); MWH (2003).

[2] Lifetime individual excess cancer risk denotes the incremental lifetime cancer risk imposed to the impacted receptors due to the stack emissions from the STF operation.

[3] 0.05mg/m³ as the limit for total concentration of Cd and Tl; 0.5mg/m³ as the limit for total concentration of Sb, As, Pb, Co, Cr, Mn, V and Ni.

[4] Unit risk factors, air quality standards/occupational exposure limit value for long term COC exposure as well as exposure limits and reference level for acute COC exposure.